A couple questions about replacing caps..

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sam
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Re: A couple questions about replacing caps..

Post by sam » Sun Oct 03, 2010 8:41 pm

I have seen this green crinkly board in a ob-1 i fixed..It looked awful but it was ok.

I once had to clean a very dirty board on my odyssey and i used a mild detergent on a sponge and dried it with kitchen roll and Q tips...I let it dry out for a day in the sun...Looks and works like new.

I always replace the electrolytic and tantalum caps.

It's good to replace the cap with a higher voltage rating that will fit in.

Don't change the cap values.. :idea:
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Re: A couple questions about replacing caps..

Post by sqweebking » Sun Oct 03, 2010 10:05 pm

It makes me feel a little better hearing that a couple of you have seen this crinkled pcb before. Like I said the traces still feel sturdy and don't appear to be cracked anywhere so I went ahead w/ cleaning. I wet the board with some hot water/light detergent mix then rinsed it all off with even hotter water. Blew out the pots with compressed out and it now sits propped up with 2 fans blowing on it.

So at this point it looks like I should only be replacing the 2 deformed white polyester caps and all the electrolytic caps. Does everyone agree that the caps with flaking paint are okay or should the be done as well? It looks like all these caps are available for cheap but I dont want to replace more than necessary.

Thanks again for all the good info.

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Re: A couple questions about replacing caps..

Post by Mooger5 » Sun Oct 03, 2010 11:02 pm

Good news then. Poly caps are robust. Although I´ve never seen that happen before, common sense tells there´s nothing wrong with them, it´s just the paint coming off.
Anyway I have a capacitance meter so I´d of course check the values of one or two just for piece of mind...

The tuning problems and the drift happening after a while could be due to some dry solder joint.

I replaced some electrolytic caps in my Rogue, not all, with the blue axials from BC Components. They´re good quality caps. I opted for axials to make sure there would be enough clearance to attach the board to the front panel.

I checked the link where I saw the filter mod and it doesn´t work, but I remember it. There´s one polyester coupling cap before the filter. The value is 100n, the author claimed is too low to pass the low frequencies, so it acts as a HPF. A 100u 63v electrolytic was suggested. May be overkill and cause audible thumps. Probably a 10u would suffice.
So it´s meant as a definitive tweak, an upgrade for the Micro to sound bassier.
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Re: A couple questions about replacing caps..

Post by sqweebking » Mon Oct 04, 2010 3:15 am

The filter mod is interesting and ill probably attempt it in the future. For now im having trouble finding the Tantalum caps I need.

Heres what im looking for: (all axial leads, 10% tolerance)
Series 150D:
3x 1.5uF 20v
1x 2.7uF 20v
Series T322:
2x 6.8uF 35v
2x 6.8uF 20v

I found and ordered the electros from mouser.com I searched for the tants there, digikey and several other places with no luck. Can these be substituted for other caps or do I have to wait the 7 weeks lead-time?

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Re: A couple questions about replacing caps..

Post by Hybrid88 » Mon Oct 04, 2010 7:59 am

rhino wrote:...My method of cleaning dirty boards is to pour near-boiling water from a tea kettle over the board (in the sink) then shake and let air dry.

EDIT: I use distilled water.
But why use such hot water? Wouldn't that just increase the chance of heat shock and possible cracking of solder joints and component body damage? I'm not being critical, if it works for you then that's fine but I'd much rather opt for the metho/toothbrush followed by water rinse method personally.

Also if the water is close to boiling (ie. around 100 deg C) then wouldn't that be damaging to the caps which are usually rated at 85 deg C for the older types found in a lot of vintage gear?

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Re: A couple questions about replacing caps..

Post by snod_donkey » Mon Oct 04, 2010 10:27 am

Looking at your pics i would say the board looks in good clean condition as it is anyway. Nothing there that would make me want to do anything too drastic. I would most definatly NOT put it in the dish washer

You would be better off just using a paint brush to remove any dust on the component side of the board and if there is any c**p stuck anywhere a bit of meths should do the trick. Dont use too much as it can leave a white deposit behind which looks even werse. Its far too easy to go over the top and make things werse than they are now....

You would most likely destroy any pots with boiling water or the dish washer as it will remove any grease... dont do it!!

As for those tracks with the crinkles in there is nothing wrong with those at all. All that is is the green solder resist raised on the tracks. This has nothing to do with the tracks themselves. The reason it is there is so when the soldering is done in the factory it makes it hard to do short circuits. "Solder Resist" - Designed for flow soldering techniques originaly. I would only be concerned if they looked like they had been getting hot

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Re: A couple questions about replacing caps..

Post by cornutt » Mon Oct 04, 2010 6:20 pm

Yeah, I recall seeing a lot of that green crinkly solder mask back in the '80s. Must have been something about the process used back then. Nothing wrong with it; it just looks funny.

My take on washing the board: don't. It doesn't look particularly bad in the photos, and as others have pointed out, washing will probably damage those pots. If you are having problems with sample-and-hold sag, locate the S&H holding capacitor on the board and clean the area around it with a bit of alcohol and an old toothbrush.
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Re: A couple questions about replacing caps..

Post by sqweebking » Tue Oct 05, 2010 12:08 am

I guess I should have held out on cleaning the board a little while longer, why would water damage pots? Would they be fine if thoroughly flushed and dried afterwards? I wanted to clean the board up because it had some greasy/sticky sections where debris had fallen on and looked like it was starting to oxidize on the top traces a bit. I could be wrong and it may have just been surface dust but im sort of OCD when it comes to things being clean.

Cornutt- what do you mean by S&H sag? IRCC the S&H was working fine last time I used this thing I just noticed those two square looking white caps that were deformed and they both happened to be in the S&H circuit.

..Still having trouble locating replacement Tantalum caps..

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Re: A couple questions about replacing caps..

Post by Hybrid88 » Tue Oct 05, 2010 8:26 am

sqweebking wrote:The filter mod is interesting and ill probably attempt it in the future. For now im having trouble finding the Tantalum caps I need.

Heres what im looking for: (all axial leads, 10% tolerance)
Series 150D:
3x 1.5uF 20v
1x 2.7uF 20v
Series T322:
2x 6.8uF 35v
2x 6.8uF 20v
I have no idea what difference the "Series" would make, if any, but as was said earlier it doesn't matter in the slightest if you go over the voltage rating for the cap, not surprisingly it's the Capcitance that is the critical value here, in fact if anything it's better to have a higher voltage rating on the replacement. Tolerance is also pretty secondary, in fact the originals used in vintage synths are probably more out of tolerance than new ones so the difference is negligible anyway. New caps are pretty accurate in value compared to the specs of vintage ones, especially considering that you're replacing ones that have been there for 30 yrs.

sqweebking wrote:I found and ordered the electros from mouser.com I searched for the tants there, digikey and several other places with no luck. Can these be substituted for other caps or do I have to wait the 7 weeks lead-time?
You could replace the tants with poly's or electro's but It's be preferable to replace like with like, trust me 7 weeks is nothing, I have just placed an order from mouser and some parts don't come into stock until 30th March 2011 - yeah, welcome to electronics - an exercise in patience. :?

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Re: A couple questions about replacing caps..

Post by Mooger5 » Tue Oct 05, 2010 2:40 pm

The reason tantalums are used is higher capacitance on a smaller footprint. I don´t know if modern ones are better, but some vintage ones short when they go wrong. I´d use electrolytics instead.

Some capacitance values are not critical. Best thing to do if you don´t want to wait IMO is to look in the schematic what the caps are for, and where possible use the next value available. Also check other sources such as Farnell or even Ebay retailers.

I used tap water and detergent to wash my Rogue. Then I sprayed the pots, sliders, switches and kbd contacts with a contact cleaner for electronics. It cleans and lubes and doesn´t damage plastics like WD-40 and others. Still going strong. No parasitic noises or weird things happening.
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Re: A couple questions about replacing caps..

Post by snod_donkey » Wed Oct 06, 2010 12:15 am

Mooger5 wrote:The reason tantalums are used is higher capacitance on a smaller footprint. I don´t know if modern ones are better, but some vintage ones short when they go wrong. I´d use electrolytics instead..
This is wrong......... Yes they can be used as they are smaller but they are a very reliable cap. An electrolytic cap is far more likely to go wrong than a tant, its just when a tant does go wrong it can fail all together. Tants do not lose any capacitance over time like an electrolytic does and its tolerance is excellent unlike electrolytics

Tant capacitors are far more expensive and in most cases were used because of the elecrical characteristics. If the caps are say on power rails for smoothing then you could change for electroloytics but if anything to do with osc's or timing circuits like ADSR EG then you must use tants to replace these. There is alot of differance how they work

Example - You can get a 47uf tant and its capacitance will be 47uf - You can get a 47uf electrolytic and its capacitance could be 20uf... when this is in a synth circuit that can make a h**l of a differance

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Re: A couple questions about replacing caps..

Post by Mooger5 » Wed Oct 06, 2010 12:58 am

From what I´ve read, subbing old tantalums is almost obligatory. Never saw electrolytics used as oscillator timing caps, or tantalums for that matter. Think you´ll find polyesters there, because the capacitances are very low and they´re not as sensitive to changes in temperature as ceramics. In the adsr if a 47uf is to be used and you put an electrolytic with 20% tolerance worst case will be 40uf. Means a release time of 8 sec instead of 10, nothing "dangerous". Measuring 20u out of a 47u electrolytic is almost 50% tolerance. I don´t think you´ll find a new electrolytic like that.
Power supply smoothing, rail decoupling and AC coupling, that´s where I´d use the next available values. I haven´t looked at the schematic yet, but it will be interesting to see where are the tantalums specified.
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Re: A couple questions about replacing caps..

Post by sqweebking » Wed Oct 06, 2010 1:34 am

I count 8 tants in the whole synth, 4 are certainly to do with the power supply, two more in the env generator, one at the beginning of the the modulation circuit and another at the beginning of the oscillator circuit. I assume they all have something to do with power smoothing or decoupling?

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Re: A couple questions about replacing caps..

Post by sqweebking » Wed Oct 06, 2010 1:40 am

Also a book I have states that tantalums are very closely related to electrolytic but basically are just smaller, more precise (lower tolerance), and less susceptible to noise. That said I think modern electros should perform just as good if not better than vintage tants given that the tolerances are less than or equal to the originals. Hows my logic?

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Re: A couple questions about replacing caps..

Post by Mooger5 » Wed Oct 06, 2010 2:00 am

Good. I don´t think Moog would design something that relied solely on what tantalums win over electrolytics but space saving. That said, I wonder if lower ESR would make my Rogue´s attack faster than 4ml sec (edit).
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